1. Field of the Invention
The present invention relates to a portable apparatus adapted for field machining of pipe, e.g., threading, rethreading, facing, refacing, etc. More particularly, the present invention pertains to a portable pipe machining apparatus, wherein the desired taper and thread pitch of a pipe end may be established by the engagement of interchangeable gear assemblies.
2. Description of the Prior Art
Sections of pipe are frequently connected for various purposes. Further, these pipe sections may be connected in several ways depending on the desired application. Many pipe sections are connected by a threaded joint in which external threads at the end of one section of pipe engage internal threads of another section. In drilling for oil and gas for example, such threaded pipe joints are used to join sections of drill pipe in a drill string which extend from the drilling rig down to the drill bit.
The seal between adjacent drill string pipe sections is usually provided by metal to metal engagement of a shoulder on the male or pin end of a pipe and the annular end face of the female or box end of the adjacent pipe. To maintain an effective downhole oil or gas drilling or recovery program, it is important that this seal between the pipe sections be maintained. Due to the hostile environment and rough handling of drill pipe, however, these seal faces and pipe threads are frequently damaged. In the past, damaged pipe sections were sent to a machine shop for refacing and/or rethreading. Since repair of the damaged pipe necessitated transport from the field to the machine shop and back to the field, this refacing and/or rethreading process was often quite costly.
In recent years, portable machines have been developed for refacing of damaged pipe joints. Examples of such portable refacing machines may be seen in U.S. Pat. Nos. 3,124,024; 3,181,398; 3,691,882; 3,717,055; 4,130,034 and 4,149,436. Most of these prior art machines utilize some type of support or mandrel which is attached to the pipe to be machined by engagement with the threads thereof. Some type of cutting tool is then provided which, upon proper rotation and feeding, cuts a new surface or face on the pipe joint.
Disadvantages of such prior art devices include their restricted application to the resurfacing of a pipe joint. If the threads of a pipe joint are damaged or worn, or if it becomes necessary to sever off a portion of the pipe joint and cut new threads and faces thereon, such portable facing machines are inadequate since they are not capable of field rethreading a virgin pipe section.
Also available in the art are portable machines adapted to utilize a cutting die such that threads may be cut on a pipe end Such devices however, are generally useful only for small diameter (&lt;3") pipe, since for larger diameter materials, an unduly large amount of torque is required, thus necessitating the presence of large compressors or drive engines. Further, threads produced as a result of such die type operations have generally been of unacceptably poor quality since dies have a tendency to "tear" the metal pipe surface, thus producing a nonsymmetrical, ragged thread.